Method and means for improving the operation under partial loads of a steam gas plant including a gas turbine and a steam turbine with a steam generator at the downstream end

ABSTRACT

A steam gas plant comprising a gas turbine, a steam generator with burners fed by the exhaust gases of the gas turbine a steam turbine fed by the steam generator wherein steam is extracted at various points of the steam turbine to feed a deaerator receiving water from water heaters and returning the water to the steam generator, the extracted steam being fed into the deaerator through channels controlled by nonreturn valves and, in at least one of such channels a gate controlled by the pressure prevailing in the deaerator so as to maintain the pressure substantially constant.

United States Patent [1 1 .Vidal et al.

METHOD AND MEANS FOR IMPROVING THE OPERATION UNDER PARTIAL LOADS OF A STEAM GAS PLANT INCLUDING A GAS TURBINE AND A STEAM TURBINE WITH A STEAM GENERATOR AT THE DOWNSTREAM END Inventors: Jean Vidal, Ville D'Avray; Paul Henri Lugand, Cravanche; Jacques Lemoine; Jean Parisot, both of Paris,

all of France Assignees: Societe General De Constructions Electrique Et Mecaniques (Alsthom); Stein Industrie, Paris, France Filed: May 14, 1970 1' Appl. Na s-7,116

Foreign Application Priority Data I May 14, 1969 France. 6914334 US. Cl. .l 60/67Q60/l07 Int. Cl. Folk 7/44, F22d 5/00 Field of Search 60/3918 B, 67 105 [451 July 3, 1973 [56] References Cited 7 UNITED STATES PATENTS 3,362,164 1/1968 Rudd 60/105 3,572,036 3/1971 Beckman et al.. 60/105 X 1,790,154 1/1931 Kasley 60/67 X 2,605,610 8/1952 Hermitte et al.. 60/39.l8 B Sheldon 60/39.!8 8

Primary ExaminerMartin P. Schwadron Assistant Examiner- Allen M. Ostrager Attorney-Arnold Robinson [5 7] ABSTRACT A steam gas plant comprising a gas turbine. a steam generator with burners fed by the exhaust gases of the gas turbinea steam turbinefed by the steam generator wherein steam is extracted at various points of the steam turbine to feed adeaerator receiving water from water heaters and returning the water to the steam generator, the extracted steam beingfed into the deaerator through channels controlledby nonreturn valves and, in at least one of such channels a gate controlled by the pressure prevailing in the deaerator so as to maintain the pressure substantially. constant.

-2 Claims l Drawing Figure METHOD AND MEANS FOR IMPROVING THE OPERATION UNDER PARTIAL LOADS OFA STEAM GAS PLANT INCLUDING A GAS TURBINE AND A STEAM TURBINE WITH A STEAM GENERATOR AT THE DOWNSTREAM END Our invention has for its object improvements in steam gas plants including a gas turbine, a steam turbine with a steam generator at the downstream end and wherein one or more gas turbines are connected through their outputs with the burners of one or more steam generators while one or more steam turbines are provided with heat exchangers for reheating the feed water for thesteam generator or generators. v

I Our invention has more particularly for its object a method for operating such a plant so as to ensure in particular efficient utilisation of the entire plant under partial loads.

Our improved method consists in a deaerator receiving the water passing out of one or more heaters fed with steam extracted from different stages of the steam turbine so as to maintain a substantially constant pressure regardless of the load on the steam turbine.

Our invention has also for its object a plant of the above-disclosed type adapted to execute the abovementioned method. According to our invention the deaerator receiving the water from one or more heaters is connected with several stages of the steam turbine through extracting channels in each of which is inserted a non-return valve while a number of said channels are provided with a valve or gate controlled by the pressure prevailing in the deaerator so as to maintain the pressure substantially constant.

There is described hereinafter by way of example and in a non-limiting sense an embodiment of our improved plant, reference being made to the single FIGURE of the accompanying drawing which illustrates the plant diagrammatically.

Our improved plant includes as shown three gas turbines 1 fed with fuel at 2 and sending their exhaust gases into the burners of a steam generator 3 through the agency of three corresponding cut-off dampers 4.

' The exhaust gases, containing large amounts of oxygen, provide means for burning within the steam generator the fuel introduced into the generator at 5.

The steam generator 3 includes a superheater 6, a reheater 7 and three e conomizers 8, 9 and 10. The flue gases pass in succession through the different parts before'they are exhausted through the chimney 11.

The plant includes also a two-stage steam turbine consisting of two stages or groups of stages 12a and 12b. The input of the first stage or groupof. stages 12a is connected with the output of the superheater 6 while its output opens into the input of the reheater 7. The input into the second stage or group of stages 12b is connected with the output of the reheater 7. The output of the second group of stages 12b of the steam turbine is connected with the input of a pump 13 through the agency of a condenser, l4. At the output of the pump 13 the condensed water is sent into a water heater l5 fed by steam produced by the first extraction port S1 in the turbine. The stream of water passing out of the water heater 15 is divided into two fractions of which one is heated in the economizer l0 and the other passes through two water heaters 16 and 17 fed respectively with steam passing out of two further extraction portsSZ and S3 in the turbine. The water passing out of the water heater 17 is mixed with that passing out of the economizer l0 and is sent into the deaerator 18 which is fed by steam fed off the extractingport S4 through a non-return valve l9or from the extracting port S5 through a non-return valve 20 associated with a gate 21 or from steam issuing from the output of the first group of stages 12a through a non-return valve 22 associated with a gate 23. At the output end of the deaerator 18 the stream of water is sucked in by a feed pump 24. The pump delivers the water into the input of the steam generator 3 through the agency of a water heater 25 and an economizer 9, the economizer 9 being inserted in parallel with the water heater 25.

The gates 21 and 23 are controlled by the pressure prevailing in the deaerator 18, measured by an instrument 26 so that, if the pressure in the deaerator drops the gate 21 opens and, if the steam tapped off the extraction port S5 is not sufficient for maintaining the pressure in the deaerator at the desired value, the gate 23 in turn opens.

The non-return valves 19, 20 and 22 are designed in a manner such that they allow the steam to pass only towards the deaerator and prevent the steam from passing out of the group of stages 12a from entering the turbine through the extraction ports S4 and S5.

Lastly a main alternator 26a is connected wih. the shaft of the turbine 12a, 12b.

It is a well-known fact that in such a type of plant, the deaerator 18 operates efficiently if the feed water reaches it at a temperature lower than the saturating temperature corresponding to the pressure of the extracted steam feeding it. Of course when the deaerator is fed only by a-single extraction port, the temperature drops simultaneously with the load and with the pressure of the extracted steam.

On'the other hand in the plant described, to retain suitable efficiency the gas turbine 1 sends into the.

for partial loads, this results in the temperature of the water at the output end of the economizer l0 increasing when the load decreases. This tendency may be cortected by a modification in the subdivision of the stream of water between the heaters 16 and 17 and the economizer 10 when the load varies but the effectiveness such a step is limited and it is of course of considerable interest to feed the deaerator for lower loads with water at a temperature as high as possible.

This result is achieved with the plant according to our invention whereinthe gates 21 and 23, controlled by the pressure in the deaerator allow the latter to be fed with steam from different points so that a substantially constant pressure is maintained for all loads. Consequently whatever the load may be the deaerator is fed by water at a constant temperature.

This allows on the one hand operation of the plant under partial loads with a greater exchange of heat in the economizer 10 than in the case of a conventional deaerator and this improves the general efficiency of.

This second consequence allows the plant to be operative with all the gas turbines operating, within a range of loads which is sufficiently large for most requirements to be satisfied. The gas turbines are then seldom stopped.

This is of considerable interest since it is a wellknown fact that the stopping of gas turbines reduces the life of the blades of the turbine and of the compressor because of the rapid changes in temperature arising during such a stoppage.

Our method for operating the deaerator in a steamgas plant provides a reduction in the frequency of overhauling the gas turbines and also in their maintenance cost.

In brief, our improved method shows in particular the following advantages it produces an improved general efficiency for the plant under partial loads since it allows an increase in the exchanges in the economizer it allows a reduction in the frequency of overhauling the gas turbines and their maintenance cost, whereby the operation of the plant is extended during low loads with three gas turbines operating under full load.

Obviously our invention is not limited to the embodiment described and it covers all the modifications thereof falling within the scope of the accompanying claims.

What we claim is:

1; In a method for operating a steam gas plant including a gas turbine, a steam turbine with a steam generator at the downstream end, a deaerator and heat exchangers including at least one water heater and at least one economizer feeding water into said deaerator, the steps consisting in extracting steam from a plurality of different points of said steam turbine and feeding said extracted steam to said deaerator, the extraction of said steam being controlled by the pressure in said deaerator thereby to maintain said pressure in said deaerator substantially constant for all loads on the steam turbine.

2. In a steam gas plant including at least one gas turbine, at least one steam generator with burnersfed by the exhaust of said gas turbine, at least one steam turbine fed by the steam of said steam generator and heat exchangers including at least one water heater and at least one economizer for the water feeding said steam generator, the provision of a deaerator located between said heat exchangers and said steam generator, a plurality of extracting channels adapted to feed said deaerator with steam from a plurality of different points of said steam turbine, a non-return valve in each of said channels, and a gate inserted in at least one of said channels and controlled by the pressure in said deaerator to maintain a substantially constant pressure in said deaerator. 

1. In a method for operating a steam gas plant including a gas turbine, a steam turbine with a steam generator at the downstream end, a deaerator and heat exchangers including at least one water heater and at least one economizer feeding water into said deaerator, the steps consisting in extracting steam from a plurality of different points of said steam turbine and feeding said extracted steam to said deaerator, the extraction of said steam being controlled by the pressure in said deaerator thereby to maintain said pressure in said deaerator substantially constant for all loads on the steam turbine.
 2. In a steam gas plant including at least one gas turbine, at least one steam generator with burners fed by the exhaust of said gas turbine, at least one steam turbine fed by the steam of said steam generator and heat exchangers including at least one water heater and at least one economizer for the water feeding said steam generator, the provision of a deaerator located between said heat exchangers and said steam generator, a plurality of extracting channels adapted to feed said deaerator with steam from a plurality of different points of said steam turbine, a non-return valve in each of said channels, and a gate inserted in at least one of said channels and controlled by the pressure in said deaerator to maintain a substantially constant pressure in said deaerator. 